Waste heat grading recovery and cold and heat coupling combined supply system of combined cycle unit

Abstract

The invention discloses a combined cycle unit waste heat graded recovery and cold and heat coupling combined supply system which is characterized in that an absorption heat pump is provided with a first external heat exchange loop, and the temperature of an external heat source medium is increased through the absorption heat pump; the second external heat exchange loop enables the external heat source medium to pass through the absorption heat pump, and the temperature of the medium is reduced; the system further comprises a grading recovery loop for low-grade heat source heat. The grading heat exchanger at least comprises a group of grading heat exchangers which respectively exchange heat with the first external heat exchange loop and the second external heat exchange loop, so that the temperature of the low-grade heat source is further reduced after the low-grade heat source passes through the grading heat exchanger. According to the combined cycle unit waste heat graded recovery and cold and heat coupling combined supply system, part of heating water is heated firstly, and the rest heating water enters the refrigerating machine. Flue gas cooling is also divided into two stages, heat supply network water is firstly used for precooling, and then an evaporator is used for further cooling. Therefore, the heat utilization rate is improved, and the discharge temperature is reduced.

Description

Technical Field

[0001] This invention relates to the field of waste heat recovery technology for combined cycle units, specifically to a combined cycle unit waste heat staged recovery and combined cooling and heating system. Background Technology

[0002] Combined cycle units mainly refer to gas-steam combined cycle units, which are power plants that integrate gas turbine cycles and steam turbine cycles. The gas turbine draws in air from the compressor, compresses it, and sends it into the combustion chamber, where fuel (such as oil or natural gas) is burned to produce high-temperature, high-pressure gas. This gas then expands in the gas turbine to generate electricity. The exhaust temperature of the gas turbine is typically around 450-650℃. A waste heat boiler is used to recover heat from the high-temperature exhaust gas from the gas turbine, using this heat to generate steam. The steam generated by the waste heat boiler expands in the steam turbine to drive a generator to produce electricity. In existing technologies, the flue gas generated by the waste heat boiler at around 100℃ is usually directly discharged. To effectively utilize this low-temperature waste heat, traditional technologies employ the following utilization methods and their shortcomings, for example: Option A: Directly utilizes waste heat from flue gas to drive a lithium bromide chiller for power generation or cooling, but it is not coordinated with the heating system, resulting in the waste heat not being utilized in a graded manner and limiting thermal efficiency.

[0003] Option B: Directly heats the heating return water through a heat exchanger, but does not solve the problem of deep utilization of low-temperature waste heat (such as flue gas below 100℃), and the emission temperature is still higher than 50℃, which does not meet environmental protection requirements.

[0004] Option C: A series system of "refrigeration unit + waste heat boiler" is adopted, but the equipment is complex and costly, and it does not achieve multi-stage distribution of waste heat and dynamic balance of combined cooling and heating.

[0005] In summary, current technologies for waste heat utilization are limited to a single grade and do not employ tiered utilization based on flue gas temperature gradients (e.g., high-temperature heating and low-temperature cooling), resulting in low energy conversion efficiency. Insufficient coupling of heating and cooling loads leads to independent operation of heating and cooling systems, lacking flexibility in waste heat distribution, and causing large fluctuations in heating network water temperature or wasted cooling capacity. Traditional waste heat utilization methods struggle to reduce flue gas temperature below 30°C, resulting in non-compliance with emission temperature standards and significant environmental pressure.

[0006] In view of the above, it is necessary to propose a combined cycle unit waste heat staged recovery and cooling-heat coupling system to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects in the existing technology and provide a combined cycle unit waste heat recovery and cooling-heating coupling system.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: a combined cycle unit waste heat staged recovery and cold and heat coupling system, including an absorption heat pump, wherein the absorption heat pump is provided with a first external heat exchange circuit and a second external heat exchange circuit, and drives a heat source circuit; The driving heat source circuit provides evaporation driving force for the absorption heat pump; The first external heat exchange circuit causes the external heat source medium to rise in temperature via an absorption heat pump. The second external heat exchange circuit causes the external heat source medium to pass through an absorption heat pump, thus reducing the medium temperature. It also includes a graded heat recovery loop for low-grade heat sources; it includes at least one set of graded heat exchangers, which exchange heat with the first external heat exchange loop and the second external heat exchange loop respectively, so that the temperature of the low-grade heat source is further reduced after passing through the graded heat exchangers.

[0009] Furthermore, the driving heat source circuit enters the generator of the absorption heat pump, the first external heat exchange circuit sequentially enters the absorber and condenser of the absorption heat pump, and the second external heat exchange circuit enters the evaporator of the absorption heat pump.

[0010] Furthermore, the low-grade heat source is gas turbine flue gas; the staged heat exchanger includes a heating network water-flue gas heat exchanger and an intermediate water-flue gas heat exchanger. The gas turbine flue gas undergoes primary heat exchange with a first external heat exchange loop in the heating network water-flue gas heat exchanger, and then undergoes secondary heat exchange with a second external heat exchange loop in the intermediate water-flue gas heat exchanger.

[0011] Furthermore, the first external heat exchange circuit is provided with a flue gas heat exchange branch and a heat pump heat exchange branch in parallel. The flue gas heat exchange branch enters the heating network water flue gas heat exchanger, and the heat pump heat exchange branch enters the absorption heat pump. The second external heat exchange circuit is an intermediate water circulation pipeline installed between the evaporator and the intermediate water flue gas heat exchanger.

[0012] Furthermore, the low-grade heat source is the steam condensate that flows out of the generator from the driving heat source circuit; the driving steam performs a first-stage heat exchange with the generator, then a second-stage heat exchange with the first external heat exchange circuit, and subsequently a third-stage heat exchange with the second external heat exchange circuit.

[0013] Furthermore, the staged heat exchanger includes a heat network water heat exchanger and an intermediate water heat exchanger. The steam condensate undergoes secondary heat exchange with the first external heat exchange loop in the heat network water heat exchanger, and then undergoes tertiary heat exchange with the second external heat exchange loop in the intermediate water heat exchanger.

[0014] Furthermore, the graded recovery loop includes a heat exchanger for a heating network water, in which the steam condensate undergoes secondary heat exchange with the first external heat exchange loop, and the steam pipe flowing out of the heat exchanger forms a second external heat exchange loop to enter the absorption heat pump and undergo tertiary heat exchange with the evaporator.

[0015] Furthermore, the graded recovery loop includes two sets of graded heat exchangers arranged in parallel. One set consists of a heat network water-flue gas heat exchanger and an intermediate water-flue gas heat exchanger connected in series with gas turbine flue gas, and the other set consists of a heat network water heat exchanger and an intermediate water heat exchanger connected in series with steam condensate.

[0016] Furthermore, the first external heat exchange circuit has three sets of parallel branch circuits, one of which enters the absorption heat pump, the second enters the heating network flue gas heat exchanger, and the third enters the heating network water heat exchanger; the second external heat exchange circuit has two sets of parallel branch circuits, and an intermediate water circulation circuit is established between the two sets of branch circuits and the evaporator, one of the two sets of parallel branch circuits entering the intermediate water flue gas heat exchanger and the other entering the intermediate water heat exchanger.

[0017] The advantages and beneficial effects of this invention are as follows: This invention provides a combined cycle unit waste heat recovery and cooling-heating coupling system. It first heats a portion of the heating water, with the remainder entering the chiller. Flue gas cooling is also two-stage: first, pre-cooling with heating network water, and then further cooling with an evaporator. This improves heat utilization efficiency and reduces emission temperature. In contrast, traditional methods directly allow flue gas to enter the chiller without first diverting it for heating, resulting in insufficient heating or excessive chiller load. Furthermore, the lack of staged flue gas cooling leads to insufficient waste heat recovery and still relatively high emission temperatures, failing to meet environmental protection requirements.

[0018] This invention directly heats a portion of the heating pipes with a low-grade heat source (primary heating), reducing the load on the lithium bromide heat pump; the remaining flue gas is fed into the lithium bromide chiller generator to drive the refrigeration cycle to generate cooling capacity, while simultaneously reheating the heating return water (secondary heating), and finally the cold and hot flows are combined and output, forming a graded utilization of waste heat.

[0019] The heating return water is used to initially cool the low-grade heat source and increase the temperature of the heating network water (100℃→60℃), forming a primary heating network water pre-cooling process. The low-grade waste heat is further absorbed by the chiller evaporator (60℃→30℃), achieving compliance with cooling output and discharge standards. This multi-stage cooling and discharge process creates a cold-heat coupling between the low-grade heat source provided by the combined cycle unit and the heating pipeline, improving waste heat recovery efficiency, reducing discharge temperature, and enhancing the integration of combined cooling and heating. Attached Figure Description

[0020] Figure 1This is a schematic flowchart of the first embodiment of a combined cycle unit waste heat staged recovery and cold and heat coupling system of the present invention; Figure 2 This is a schematic flowchart of the second embodiment of a combined cycle unit waste heat staged recovery and cold and heat coupling system of the present invention; Figure 3 This is a schematic flowchart of the third embodiment of a combined cycle unit waste heat staged recovery and cold and heat coupling system of the present invention; Figure 4 This is a schematic flowchart of the fourth embodiment of a combined cycle unit waste heat staged recovery and cold and heat coupling system of the present invention; In the diagram: 1. Absorption heat pump; 2. First external heat exchange loop; 3. Second external heat exchange loop; 4. Drive heat source loop; 5. Staged recovery loop; 6. Generator; 7. Absorber; 8. Condenser; 9. Evaporator; 10. Gas turbine flue gas; 11. Heat network water-flue gas heat exchanger; 12. Intermediate water-flue gas heat exchanger; 13. Flue gas heat exchange branch; 14. Heat pump heat exchange branch; 15. Intermediate water circulation pipeline; 16. Steam condensate; 17. Heat network water heat exchanger; 18. Intermediate water heat exchanger; 19. Heat network water heat exchange branch. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0022] Example 1: A combined cycle unit waste heat staged recovery and combined cooling and heating system, such as Figure 1 As shown, it includes an absorption heat pump 1, which is a device that uses lithium bromide solution as an absorbent and water as a refrigerant to transfer heat energy through an absorption cycle. In this embodiment, the absorption heat pump 1 mainly includes an evaporator 9, an absorber 7, a generator 6, and a condenser 8. The heat exchange circuits connected to the external side of the absorption heat pump 1 include: a driving heat source circuit 4, which provides evaporation driving force to the absorption heat pump 1; a first external heat exchange circuit 2, which causes the external heat source medium to pass through the absorption heat pump 1 and increase the medium temperature; and a second external heat exchange circuit 3, which causes the external heat source medium to pass through the absorption heat pump 1 and decrease the medium temperature.

[0023] Specifically, in this embodiment, the first external heat exchange loop 2 is a heating pipe. The heating pipe is heated by the absorption heat pump 1 and then supplied. Specifically, the first external heat exchange loop 2 sequentially enters the absorber 7 and condenser 8 of the absorption heat pump 1, so that the temperature of the heating network water in the heating pipe increases after flowing out of the absorption heat pump 1. The second external heat exchange loop 3 enters the evaporator 9 of the absorption heat pump 1. Specifically, the second external heat exchange loop 3 is an intermediate water circulation pipe 15 set between the evaporator 9 and the intermediate water flue gas heat exchanger 12. In this embodiment, an intermediate water circulation loop is set up, which is driven by a water pump to circulate. The intermediate water temperature decreases after passing through the evaporator 9. After entering the intermediate water heat exchanger 18, the intermediate water exchanges heat with the gas turbine flue gas 10 and then returns to the evaporator 9 to form a circulation.

[0024] In actual use, the return water temperature of the heating pipes is approximately 55℃, while the supply water temperature rises to approximately 75℃ after heating. The absorption heat pump 1 recovers heat from the low-grade heat source in the combined cycle unit and heats the circulating water in the heating pipes to achieve heating, thus utilizing the low-grade heat source. To ensure full recovery and utilization of the low-grade heat source, a graded heat recovery loop 5 is also provided.

[0025] In this embodiment, the staged heat recovery loop 5 is equipped with a set of staged heat exchangers. These staged heat exchangers perform multi-stage recovery and utilization of heat from low-grade heat sources. Specifically, the target of low-grade heat source recovery in this embodiment is the gas turbine flue gas 10. The temperature of the gas turbine flue gas 10 is 80~100℃. In existing technologies, it is usually directly emitted, resulting in a significant waste of heat resources. In this embodiment, the staged heat exchangers include a heat network water-flue gas heat exchanger 11 and an intermediate water-flue gas heat exchanger 12. The gas turbine flue gas 10 undergoes primary heat exchange with the first external heat exchange loop 2 in the heat network water-flue gas heat exchanger 11, and then undergoes secondary heat exchange with the second external heat exchange loop 3 in the intermediate water-flue gas heat exchanger 12. Specifically, the heating pipeline, i.e., the first external heat exchange circuit 2, is divided into two parallel branches in actual implementation. Specifically, the first external heat exchange circuit 2 is provided with a flue gas heat exchange branch 13 and a heat pump heat exchange branch 14 in parallel. The flue gas heat exchange branch 13 enters the heating network water flue gas heat exchanger 11, and the heat pump heat exchange branch enters the absorption heat pump 1. One of the two branches enters the heating network water flue gas heat exchanger 11, and the other branch enters the absorber 7 and condenser 8 in the absorption heat pump 1. The first branch directly exchanges heat with the gas turbine flue gas 10 at 80~100℃ to achieve temperature increase, and the other part enters the absorption heat pump 1 as the second branch for temperature increase. In this way, the low-grade heat source can be separated and effectively utilized, and the heating capacity of the heating pipeline can be increased. After the gas turbine flue gas 10 is cooled once by the heat network water flue gas heat exchanger 11, it immediately enters the intermediate water flue gas heat exchanger 12 and exchanges heat with the intermediate circulating water in the intermediate water circulation pipeline 15, so that the gas turbine flue gas 10 is reduced to about 30°C before being discharged, thereby reducing the discharge temperature and improving the waste heat recovery efficiency.

[0026] In this embodiment, the staged heat exchanger exchanges heat with the first external heat exchange circuit 2 and the second external heat exchange circuit 3 respectively, so that the temperature of the low-grade heat source is further reduced after passing through the staged heat exchanger, thereby making fuller use of the heat in the low-grade heat source. After the heat of the low-grade heat source is recovered and utilized by the staged recovery circuit 5, the flue gas temperature of the gas turbine is reduced to about 30°C.

[0027] Example 2: Similar to Embodiment 1, this embodiment includes an absorption heat pump 1, a first external heat exchange loop, a second external heat exchange loop, and a heating pipe. The absorption heat pump 1 is equipped with an evaporator 9, an absorber 7, a generator 6, and a condenser 8. The first external heat exchange loop is still the heating pipe, which is divided into two parallel branch loops, including a heating network water heat exchange branch 19 and a heat pump branch. The two branch loops divert the heating network water in the heating pipe, and the water enters the heating network water heat exchanger 17 and the absorption heat pump 1 respectively, where it is heated and then merged and sent out. The second external heat exchange loop is the same as in Embodiment 1, wherein the medium water circulation pipe 15 enters the medium water heat exchanger 18.

[0028] The difference is, such as Figure 2 As shown, in this embodiment, the low-grade heat source is the steam condensate 16 flowing out of the generator 6. The temperature of this condensate is between 80 and 90°C. Specifically, the driving steam undergoes a primary heat exchange with the generator 6, followed by a secondary heat exchange with the first external heat exchange loop 2, and then a tertiary heat exchange with the second external heat exchange loop 3, thus achieving multi-stage utilization of steam heat. In this embodiment, the staged heat exchangers include a heat network water heat exchanger 17 and an intermediate water heat exchanger 18. The steam condensate 16 undergoes a secondary heat exchange with the first external heat exchange loop 2 in the heat network water heat exchanger 17, and then a tertiary heat exchange with the second external heat exchange loop 3 in the intermediate water heat exchanger 18. Finally, the temperature of the steam condensate 16 drops to about 40°C before being sent back to the power plant's steam unit for reuse in generating steam.

[0029] Example 3: This embodiment is basically the same in principle as Embodiment Two, except that Embodiment Two includes a separate second external heat exchange loop 3 and an intermediate water heat exchanger 18. An intermediate water circulation pipe 15 is installed between the intermediate water heat exchanger 18 and the evaporator 9, and a water pump is used to establish intermediate water circulation, transferring heat between the evaporator 9 and the intermediate water heat exchanger 18 through the intermediate water. This embodiment further simplifies the structure; specifically, the intermediate water heat exchanger 18 is removed, and the three-stage heat exchange of the steam condensate 16 is changed to direct heat exchange in the evaporator 9. Figure 3 As shown, the graded recovery loop 5 includes a heat exchanger 17. The steam condensate 16 undergoes secondary heat exchange with the first external heat exchange loop 2 in the heat exchanger 17. The steam pipe flowing out of the heat exchanger 17 forms the second external heat exchange loop 3 and enters the absorption heat pump 1 to undergo tertiary heat exchange with the evaporator 9.

[0030] Example 4: This implementation example Figure 4As shown, this embodiment comprehensively utilizes the low-grade heat sources of gas turbine flue gas 10 and steam condensate 16. Specifically, the staged recovery loop 5 is configured as two sets of staged heat exchangers connected in parallel. One set of staged heat exchangers is used to recover and utilize the low-grade heat source of gas turbine flue gas 10, while the other set of staged heat exchangers recovers and utilizes the low-grade heat source of steam condensate 16. It can be understood that the number of stagesd heat exchangers is not limited, and other low-grade heat sources can be introduced and corresponding staged heat exchangers can be added in parallel to form a comprehensive staged heat energy recovery and utilization of multiple low-grade heat sources, thereby improving the integration of combined cooling and heating.

[0031] like Figure 4 As shown, one of the two-stage heat exchangers consists of a heat network water-flue gas heat exchanger 11 and an intermediate water-flue gas heat exchanger 12 connected in series with gas turbine flue gas 10, and the other consists of a heat network water heat exchanger 17 and an intermediate water heat exchanger 18 connected in series with steam condensate 16. The first external heat exchange circuit 2 has three parallel branch circuits: one enters the absorption heat pump 1, the second enters the heat network water-flue gas heat exchanger 11, and the third enters the heat network water heat exchanger 17. In actual use, flow control valves can be installed on the three parallel branch circuits, and temperature sensors can be installed at the outlet of each branch circuit. When the three branch circuits converge into the main pipe, the hot water supply temperature is controlled at around 75°C. The flow control valves on each branch circuit can be automatically adjusted according to the heat load of each branch circuit, thereby achieving precise temperature control. In addition, the second external heat exchange circuit 3 in this embodiment is provided with two sets of parallel branch circuits. An intermediate water circulation circuit is established between the two sets of branch circuits and the evaporator 9. One of the two sets of parallel branch circuits enters the intermediate water flue gas heat exchanger 12 and the other enters the intermediate water heat exchanger 18.

[0032] This embodiment achieves comprehensive utilization of multiple low-grade heat sources, improves heat recovery efficiency, and allows the low-grade heat sources to directly heat a portion of the heating pipes, thereby reducing the load on the lithium bromide heat pump. The remaining low-grade heat sources exchange heat with the evaporator 9 of the lithium bromide chiller through intermediate water, driving the refrigeration cycle to generate cooling capacity, and the temperature of the low-grade heat sources is reduced again, so that the energy of the heat sources can be further recovered and utilized, thereby forming a more effective staged utilization of waste heat.

[0033] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A combined cycle unit waste heat staged recovery and combined cooling and heating system, comprising an absorption heat pump (1), characterized in that, The absorption heat pump (1) is provided with a first external heat exchange circuit (2), a second external heat exchange circuit (3), and a driving heat source circuit (4). The driving heat source circuit (4) provides evaporation driving force for the absorption heat pump (1); The first external heat exchange circuit (2) causes the external heat source medium to rise in temperature through the absorption heat pump (1); The second external heat exchange circuit (3) causes the external heat source medium to pass through the absorption heat pump (1), and the medium temperature is reduced; It also includes a graded heat recovery loop (5) for low-grade heat sources; it includes at least one set of graded heat exchangers, which exchange heat with the first external heat exchange loop (2) and the second external heat exchange loop (3) respectively, so that the temperature of the low-grade heat source is further reduced after passing through the graded heat exchangers.

2. The combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 1, characterized in that, The driving heat source circuit (4) enters the generator (6) of the absorption heat pump (1), the first external heat exchange circuit (2) enters the absorber (7) and condenser (8) of the absorption heat pump (1) in sequence, and the second external heat exchange circuit (3) enters the evaporator (9) of the absorption heat pump (1).

3. The combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 2, characterized in that, The low-grade heat source is gas turbine flue gas (10); the staged heat exchanger includes a heating network water flue gas heat exchanger (11) and an intermediate water flue gas heat exchanger (12). The gas turbine flue gas (10) undergoes primary heat exchange with the first external heat exchange loop (2) in the heating network water flue gas heat exchanger (11), and then undergoes secondary heat exchange with the second external heat exchange loop (3) in the intermediate water flue gas heat exchanger (12).

4. The combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 3, characterized in that, The first external heat exchange circuit (2) is provided with a flue gas heat exchange branch (13) and a heat pump heat exchange branch (14) in parallel. The flue gas heat exchange branch (13) enters the heat network water flue gas heat exchanger (11), and the heat pump heat exchange branch enters the absorption heat pump (1). The second external heat exchange circuit (3) is an intermediate water circulation pipeline (15) installed between the evaporator (9) and the intermediate water flue gas heat exchanger (12).

5. A combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 2 or 4, characterized in that, The low-grade heat source is the steam condensate (16) formed by the flow of the driving heat source circuit (4) out of the generator (6); the driving steam performs a first-stage heat exchange with the generator (6), then performs a second-stage heat exchange with the first external heat exchange circuit (2), and then performs a third-stage heat exchange with the second external heat exchange circuit (3).

6. A combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 5, characterized in that, The staged heat exchanger includes a heat network water heat exchanger (17) and an intermediate water heat exchanger (18). The steam condensate (16) undergoes secondary heat exchange with the first external heat exchange loop (2) in the heat network water heat exchanger (17), and then undergoes tertiary heat exchange with the second external heat exchange loop (3) in the intermediate water heat exchanger (18).

7. A combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 5, characterized in that, The graded recovery loop (5) includes a heat exchanger (17) for a heat exchanger network. The steam condensate (16) undergoes secondary heat exchange with the first external heat exchange loop (2) in the heat exchanger network (17). The steam pipe flowing out of the heat exchanger network (17) forms a second external heat exchange loop (3) and enters the absorption heat pump (1) to undergo tertiary heat exchange with the evaporator (9).

8. A combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 6, characterized in that, The graded recovery circuit (5) includes two sets of graded heat exchangers arranged in parallel. One set consists of a heat network water-flue gas heat exchanger (11) and an intermediate water-flue gas heat exchanger (12) connected in series with gas turbine flue gas (10), and the other set consists of a heat network water heat exchanger (17) and an intermediate water heat exchanger (18) connected in series with steam condensate (16).

9. A combined cycle unit waste heat staged recovery and combined cooling and heating system according to claim 8, characterized in that, The first external heat exchange circuit (2) has three sets of parallel branch circuits, one of which enters the absorption heat pump (1), the second enters the heat network water flue gas heat exchanger (11), and the third enters the heat network water heat exchanger (17); the second external heat exchange circuit (3) has two sets of parallel branch circuits, and the two sets of branch circuits establish an intermediate water circulation circuit with the evaporator (9). One of the two sets of parallel branch circuits enters the intermediate water flue gas heat exchanger (12), and the other enters the intermediate water heat exchanger (18).

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